The invention described herein relates generally to an air driven centrifuge and more particularly to an improved apparatus for holding and stabilizing such rotor during its deceleration.
In order to separate certain fluid mixtures, very high speeds of rotation are required. For example, separation of protein, viruses and other various clinical specimens require extremely high speeds of centrifugation in order to separate fractions thereof within reasonable time spans. It has been found that extremely high rotational speeds such as 150,000 r.p.m. to 200,000 r.p.m. can be obtained by rotating a centrifuge rotor on a cushion of air with pressurized air streams. An example of such as air driven centrifuge is illustrated in U.S. Pat. No. 3,456,875 issued to me on July 22, 1969.
In the case of air driven centrifuges, when the driving air has been shut down after the centrifugation of the fluid mixture, a secondary supporting supply of air must be introduced between the rotor and rotor seat to hold the rotor off the rotor seat as the rotor decelerates to a stop. However, in some present devices because of the location of the flutes on the rotor the introduction of a supporting air supply will never allow the rotor to completely stop, since this air movement across the rotor flutes will tend to continue driving the rotor slightly on the supporting air. This supporting air is generally introduced along the outer frustoconical portion of the rotor seat adjacent the location of the driving air jets.
In some instances, the orientation of the driving air jets is reversed to not only supply supporting air, but also to aid in the deceleration of the rotor to a stop. In some cases the use of the reversing air jets may cause the start of a reverse rotation of the rotor after it has stopped. Consequently, many arrangements now used do not provide a friction free cushion of air which allows the rotor to decelerate independent of any driving effects of the supporting air.
A significant problem also exists with respect to the inherent design of every rotor in addition to the characteristics of the test mixtures in the rotor, presenting certain parameters which create critical speeds where the rotor will precess, wobble or vibrate excessively while decelerating. These critical speeds are usually relatively low rotational speeds and the precession and/or wobblng can become so great as to cause the sample to be remixed or to cause the rotor to contact the sidewalls of the seat, causing the rotor to become misaligned from its rotational axis and thrash around within the centrifuge housing.
Consequently, some prior art arrangements incorporate a stabilizing means to physically contact or guide the rotor as it experiences these slow critical speeds to help eliminate the above described undesirable effects. The supporting air in these devices provide sufficient stabilization to overcome the problems encountered during the critical speeds of the rotor, but such stabilizing devices must be quite delicate in design to provide the requisite stabilizing and are subject to constant wear.
In addition, other supporting air arrangements used heretofore tend to establish a cushion of air which causes the rotor to ride somewhat high within the rotor seat. In other words, the rotor is separated from the surface of the rotor seat more than desirable, rendering the rotor more susceptible to various unstabilizing conditions and possible ejection from the rotor seat.